O365 Bypass MFA via Trusted IP

name: O365 Bypass MFA via Trusted IP
id: c783dd98-c703-4252-9e8a-f19d9f66949e
version: 13
creation_date: '2021-01-13'
modification_date: '2026-05-13'
author: Bhavin Patel, Mauricio Velazco, Splunk
status: production
type: TTP
description: The following analytic identifies instances where new IP addresses are added to the trusted IPs list in Office 365, potentially allowing users from these IPs to bypass Multi-Factor Authentication (MFA) during login. It leverages O365 audit logs, specifically focusing on events related to the modification of trusted IP settings. This activity is significant because adding trusted IPs can weaken the security posture by bypassing MFA, which is a critical security control. If confirmed malicious, this could lead to unauthorized access, compromising sensitive information and systems. Immediate investigation is required to validate the legitimacy of the IP addition.
data_source:
    - O365 Set Company Information.
search: '`o365_management_activity` Operation="Set Company Information." ModifiedProperties{}.Name=StrongAuthenticationPolicy | rex max_match=100 field=ModifiedProperties{}.NewValue "(?<ip_addresses_new_added>\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\/\d{1,2})" | rex max_match=100 field=ModifiedProperties{}.OldValue "(?<ip_addresses_old>\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\/\d{1,2})" | eval ip_addresses_old=if(isnotnull(ip_addresses_old),ip_addresses_old,"0") | mvexpand ip_addresses_new_added | where isnull(mvfind(ip_addresses_old,ip_addresses_new_added)) | fillnull | stats count min(_time) as firstTime max(_time) as lastTime values(ip_addresses_old) as ip_addresses_old by signature dest user src vendor_account vendor_product ip_addresses_new_added | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `o365_bypass_mfa_via_trusted_ip_filter`'
how_to_implement: You must install Splunk Microsoft Office 365 add-on. This search works with o365:management:activity
known_false_positives: Unless it is a special case, it is uncommon to continually update Trusted IPs to MFA configuration.
references:
    - https://i.blackhat.com/USA-20/Thursday/us-20-Bienstock-My-Cloud-Is-APTs-Cloud-Investigating-And-Defending-Office-365.pdf
    - https://attack.mitre.org/techniques/T1562/007/
    - https://learn.microsoft.com/en-us/azure/active-directory/authentication/howto-mfa-mfasettings
finding:
    title: User $user$ has added new IP addresses $ip_addresses_new_added$ to a list of trusted IPs to bypass MFA
    entity:
        field: user
        type: user
        score: 50
analytic_story:
    - Office 365 Persistence Mechanisms
asset_type: O365 Tenant
mitre_attack_id:
    - T1686.001
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: cloud
security_domain: threat